Human peripheral blood lymphocytes with augmented ADCC activity resulting from 2-day in vitro stimulation by Concanavalin A have been quantitatively assessed by flow microfluorometry for IgG Fc receptor density, affinity and distribution profiles. Analysis of 100,000 cell aliquots of Con A stimulated and control, non-stimulated cells from each of four donors revealed that 4-25% of cells bore IgG Fc receptors (FcR). Analysis of the FcR positive cells from each of the 4 donors showed that the average receptor density for a donor ranged from 65,000 to 72,000 receptors per cell, assuming that each subunit of Fc receptor ligand (dimeric anti-DNP) bound to an Fc receptor. The average binding constant per donor ranged from 1.8 to 2.6 times 10 to the 7th power (M-1). Con A stimulation did not have a consistent effect on either of these parameters, and the changes that did occur represented less than 10% of the values for control cells. All fluorescence distribution profiles of cells with fluorescence labeled Fc receptor were unimodal and nearly overlapping for Con A stimulated and control cells.